Many work situations require workers to be positioned on top of platforms or vehicles that cannot be practically protected by a guardrail system enclosing the work area. To prevent the workers from falling from such elevated positions and thereby sustaining serious or mortal injuries, various fall protection systems can be used. In general, fall arrest or fall protection systems are designed to prevent the worker from reaching an unprotected edge or to quickly stop a fall before the worker impacts a lower level. Such systems typically include an anchorage secured to a structure overhead the work area, a safety harness worn by the worker, and a flexible tether line or “lanyard” interconnecting the anchorage to the harness.
One type of fall protection system includes a trolley or other moveable anchorage that is moveably mounted on a track provided by a rigid rail installed parallel to and above, the length of the working area. A moveable anchorage is particularly useful when the work area is narrow and long, for example, on top of a line of vehicles such as buses or rail cars. In general, the moveable anchorage is designed to freely move along the rail by engaging the rail track to permit movement in a longitudinal direction but at the same time preventing the anchorage from separating from the rail or moving in a transverse direction. Consequently, the worker can freely move along the length of the work area with the lanyard being kept at a minimum length at all times so as to reduce the risk of an undesirable pendular swinging motion in the event of a fall.
Rigid rail systems can use various structural members to provide the track, such as, for example, flanged beams, slotted hollow tubes, and flat bars, with the moveable anchorage typically being a wheeled trolley. The rigid rail must be structurally supported on an overhead structure to hold the rail in place and to support the weight of the moveable anchorage and any connected workers in the event of a fall.
Most conventional rigid rail systems use a flanged beam installed in the “I” orientation, having horizontally oriented flanges and a vertically oriented web. The movable anchorage is typically a wheeled trolley having a U-shaped profile whose wheels are supported on the bottom flange straddling the web. Overhead support members are attachment to the top of the flanged-beam for attachment to an overhead structure. Orientation of the flanged beam in the “I” orientation provides the most structurally efficient rail because the greatest amount of material is concentrated at the top and the bottom of the beam to provide greatest strength and stiffness of the beam.
In another type of rigid rail system, a horizontally extending flat bar is installed with the plane of the bar being vertically oriented. The moveable anchorage is typically a wheeled trolley having a C-shaped profile and at least one set of upper and lower flanged wheels rolling on a top edge and bottom edge of the bar, respectively. The bar is supported by periodic and longitudinally spaced horizontal support members attached to a side of the bar, with the periodic support members being located at mid height of the bar so as to not interfere with free movement of the trolley past the supports. A disadvantage of the use of a bar as compared to an I-oriented flanged beam is that the bar has less torsional and transverse bending stiffness, resulting is a significant tendency to buckle in a lateral-torsional mode when subjected to a vertical load. Consequently, the bar does not participate in carrying long-span loadings. Further, to help restrain the bar from lateral-torsional buckling, the bar must be attached to closely spaced, torsionally rigid periodic supports. For example, a bar typically requires periodic support members every 3 to 6 feet, while the same length of I-oriented flanged beam typically requires a support member every 10 to 25 feet. Where overhead attachments are widely spaced, it is necessary to attach the bar to an independent and intermediate structural member, such flanged beam or a tube section, which is capable of carrying vertical loads over the span and the periodic support members are spaced therealong. In either case, the requirement for additional components for using a bar-type rail greatly increases the cost of the completed system.
In some situations, it is desirable to permit two or more workers to independently and freely traverse the entire length of a work area. The solution has been to install separate, parallel rails, with each rail having a moveable anchorage to which one of the workers is connected. Such rails can be supported by independent support members, or the separate rails can be attached to a common supporting member. For example, the MSA “twin track” Sure-Rail™ System (Pittsburgh, Pa.) comprises an assembly of two bar rail systems attached to a central and intermediate support member by periodic support plates, and the intermediate support member is supported from overhead attachments. More particularly, the horizontal periodic support members of each bar are attached to separate vertical support plates, with the support plates in turn being attached to opposing sides of the intermediate central support member. In any case, the need to install separate parallel rails represents significant manufacturing and labor costs.
There is, therefore, a need in the art for an improved rigid rail fall protection apparatus.